Chemokines and their receptors are involved in both the innate and adaptive immune response;however, inappropriate activation or expression of chemokines and receptors has been identified in several diseases such as atherosclerosis, multiple sclerosis, asthma, and rheumatoid arthritis. Although the chemokine network is crucial to host defense, little is known about the molecular mechanism of receptor activation by ligand. Chemokine receptors belong to the family of Rhodopsin-like G-protein coupled receptors (GPCRs). GPCRs are characterized by 7-transmembrane spanning helices coupled intracellularly to a heterotrimeric G-protein. Agonist-induced activation of chemokine receptors results in conformational changes that trigger downstream signaling of the G-protein. To this end, the objectives set forth in this training plan aim to elucidate the molecular mechanism of activation of the chemokine receptor, CCR1, by the chemokine agonist, MCP-3. Like many chemokines and chemokine receptors, MCP-3 and CCR1 likely play a role in the pathogenesis of inflammatory diseases that involve monocyte infiltration. The specific aims of this proposal are as follows: (1) In collaboration with the Woods lab here at UCSD, we will use enhanced deuterium exchange with Mass Spectrometry (DXMS) to identify the interaction surfaces between the MCP-3:CCR1 complex. (2) Carry out mutagenesis on the extracellular loop regions of CCR1 to identify specific residues involved in ligand binding and activation. Separately, these two approaches will provide significant insight into the chemokine receptor-ligand interactions, but taken together, they provide a comprehensive analysis of CCR1:MCP-3 interactions. Therefore, identifying and understanding these particular interactions will aid the development of small molecule antagonists of CCR1, given its involvement in several diseases. RELEVANCE TO PUBLIC HEALTH: Chemokines play a major role in our immune system response;however, inappropriate activity of chemokines and receptors can result in inflammatory diseases such as atherosclerosis, multiple sclerosis, and rheumatoid arthritis. Therefore, the structural and functional knowledge gained from these studies of the chemokine receptor will contribute to our limited understanding of chemokine receptor-ligand activity and function. This information can guide therapeutic interference strategies in the treatment of inflammatory diseases.